The present invention is concerned with instruments for measuring elevations and is particularly concerned with microcomparators for such measurements to have a resolution of better than half a micron.
Prior instruments of this type differ mainly in the amplification mechanism that is used. They may be classified into two different groups.
The first group generally includes a stop connected to a feeler piston bearing with a straight bearing rod upon the shorter arm of a lever, which is pivotally mounted in the housing. The longer arm of the lever is furnished with a cogged segment meshing with the pinion of a multiplying geartrain which actuates the display means. The amplification is the result of the geometric relationship of the lever and the geartrain.
The arrangement of a straight bearing rod bearing against a circularly shaped cam allows variations of length of the shorter arm to be compensated. Such variations are caused, for example, by a slight transversal shift of the stop due to wear of the bearing guides of the feeler-piston. Such variations adversely affect the amplification and precision of measurement.
The first group of microcomparators also have means to adjust the amplification and, therefore, the sensitivity of the device. Such devices are described, for example in Swiss Pat. No. 569 951 and include several movable cooperating mechanical parts.
Such devices suffer from the disadvantages of having a large number of movable parts positioned with great precision, which is expensive and time consuming.
Another group of microcomparators have a simpler construction. These are schematically shown in FIG. 1, where the amplification is caused by a lever having a shorter arm and a longer arm. The longer arm carries a cogged sector which directly engages a pinion which drives the indicator needle. The amplification is determined by the relation between the lengths of the arms.
Since the length of the longer arm is limited by the outer dimensions of the device, it is understood that the shorter arm must be much shorter than in the devices of the first group of comparators described above in order to obtain sufficient amplification, on the order of amplification by a factor of one thousand. Therefore, the same deviation in the stop of the same variation of the length of the shorter arm will be greatly amplified and affect the measurements being made. Furthermore if the dimension of the device is to be maintained fixed, the prior art does not allow for varying the amplification.
Therefore, the prior art has failed to provide measurement apparatus which can provide precise measurements with large amplification at reasonable costs and which can permit easy adjustment of amplification.
It is an object of the present invention to provide an instrument for elevational measurements that is economical and solves the above-mentioned problems.
Another object of the present invention is to provide a microcomparator which allows easy changing from one amplification scale to another one.
Another object of the present invention is to provide a microcomparator which may be reset at zero easily, rapidly and practically.